Expression of osteopontin coregulators in primary colorectal cancer and associated liver metastases

Abstract

Background: A transcription regulatory complex (TRC) that includes Ets1, Ets2, PEA3 and β-catenin/T-cell factors regulates osteopontin (OPN) that is implicated in colorectal cancer (CRC) dissemination. The consistency of OPN transcriptional control between primary CRC and metastases is unclear. This study investigates expression and prognostic significance of the OPN-TRC in primary human CRC and associated colorectal liver metastases (CRLM).

Methods: Osteopontin-TRC factors were assayed by digital microscopy in 38 primary CRCs and matched CRLM specimens and assessed against clinical prognosis.

Results: In primary CRC, OPN expression intensity correlated with that of its co-activators, PEA3 (r=0.600; P<0.01), Ets1 (r=0.552; P<0.01), Ets2 (r=0.521; P<0.01) and had prognostic significance. Osteopontin intensity in primary CRC inversely correlated with the interval between diagnosis and resection of CRLM. Overall OPN intensity was lower in CRLM than primary CRC and correlations with co-activators were weaker, for example, Ets1 (P=0.047), PEA3 (P=0.022) or nonsignificant (Ets2). The ratio of OPN expression in CRLM vs primary CRC had prognostic significance.

Conclusion: This study supports transcriptional control of OPN by known coregulators in both primary and secondary CRC. Weaker associations in CRLM suggest involvement of other unknown factors possibly from the liver microenvironment or resulting from additional genetic or epigenetic changes that drive tumour metastatic capability in OPN transcriptional control.

Figure 1

Digital expression analysis of OPN. An automated positive pixel count algorithm was applied to the digitally scanned annotated images. The image shown is a section of colorectal primary tumour stained for OPN visualised with DAB.

Figure 2

Osteopontin and coregulators in primary CRC and CRLM matched pairs. Consecutive sections of colorectal primary tumour and liver metastasis, illustrating the raw scanned image and the positive pixel count for each primary antibody. Line diagrams show the difference between primary tumour and matched liver metastasis for each patient.

Figure 3

Osteopontin intensity in primary CRC vs interval to liver resection. Osteopontin expression in primary CRC inversely correlates with interval between colectomy and liver resection for metastases (P=0.045; Pearson's product moment test).